Prosthetic cardiac valves can be surgically implanted to replace the main heart valves, that is the mitral and aortal valves. Such valves must open and close rapidly while imparting minimal turbulence to blood flow in the passage in which they are provided. Obviously if they are difficult to open they will increase upstream blood pressure and the load on the heart, and if they do not close fully they will allow perilous backflow. In addition if they create excessive turbulence they can cause life-threatening embolisms.
It is known to make such valves of animal tissue, neutralized to prevent rejection. Such valves can exactly mimic the action of the valves they replace, but are prone to physical breakdown and mechanical failure. Thus on the one hand there is the advantage of little increase in the likelihood of embolism, thereby eliminating anticoagulant treatment, but on the other their potentially short service life poses a constant danger for the host.
Recourse is therefore normally had to sturdier mechanical valves. A standard type comprises a cage having at one end a seat and containing a ball that can move against the seat or from it, depending on the flow direction. Such an arrangement has a service life that can be expected to last the lifetime of the host, but normally creates quite some turbulence in the blood flow it controls. To prevent thrombosis it is therefore necessary for the host to be maintained on a treatment of anticoagulants.
It is also known to use a standard flap- or disk-type check valve mounted in a collar that is sewn into the passage. The flap opens by moving into a position parallel to the flow, and closes by moving into a position across the flow and blocking the collar. Even when such a valve is equipped with two flaps to open as quickly as possible, it creates considerable turbulence just as it starts to open, normally in the first 10.degree. of pivoting. Thus thrombosis, embolisms, and hemolytic degradations are a problem.